Over the past 50 years, laundry cleaner packaging and formulations have changed significantly, with predominately powdered cleaners in cardboard boxes replaced by liquid formulations in plastic containers. While the liquid formulations work well in cold water, and solve prior issues with powder clumping and inadequate dissolution in cold water, liquids pose their own problems. With the liquid formulations comprising significant amounts of water, the packages may be large and heavy, necessitating high transportation costs. Further, the liquid detergent packages require relatively large volumes of display space at stores, and commensurate storage after purchase by consumers. Additionally, the move from paper to predominantly plastic containers has resulted in recycling issues; whereas paper recycling, including cardboard, is widely available, plastic recycling remains limited, with plastic often ending up in landfills.
Prior to the introduction of liquid laundry cleaning formulations, powdered laundry cleaners were dissolved in 10 to 40 gallons of water in washing machines, with powder formulations often leaving clumpy white particulate behind, known as detergent stains. Detergent stains are more prevalent when the powdered laundry formulation is used with warm or cold water (water that is <130 deg F. in general). With modern washers, especially high efficiency washers, using from 15 gallons (high efficiency) to 23 gallons (industry standard) of water for the entire wash cycle, it has become increasingly necessary for more soluble solid powdered laundry detergents and soaps to be available, while increasing the desirability of liquid formulations. Additional problems with soap dissolution has become more pronounced with the use of cold water washing, as soap-based laundry products require hot temperature water for good dissolution.
With the desire on the part of consumers to reduce the energy costs associated with hot water laundry cleaning, consumers shifted to cold and warm water washing. In some parts of the world, cold water washing can refer to water temperatures that are in the range of 34 deg F. and greater. Cold and warm water washing have motivated the move to liquid laundry cleaners. These, however, have their own issues with dissolution and stability, with the relatively concentrated liquid laundry cleaners requiring additives, special orders of addition of constituents for the solutions to remain stable, and high shear mixing to put some constituents into solution.
The need for more soluble and stable laundry cleaning formulations has further led to a departure from soap-based surfactants and the adoption of poly-alkoxylated surfactants, typically incorporating medium to long chain alkanes, alchohols, alkylphenols, alkylphosphates, and alkylsulfonates. These surfactants are widely used in both dry powdered and liquid detergents such as those disclosed by Brouwer et al in U.S. Pat. No. 5,990,068 (“Powder Detergent Composition Having Improved Solubility,” 1999) and Wollenweber et al in U.S. Pat. No. 5,807,502 (“Aqueous Fatty Alcohol Dispersions,” 1998). Brouwer et al disclose detergent compositions that incorporate synthetic surfactants containing from 3 to 80 ethoxy groups, and necessitating a quantity of fumaric acid as an acidulant to further boost solubility. Wollenweber et al disclose liquid detergents that incorporate both long chain fatty alcohols and alkanes with from 5 to 50 ethoxy groups with both surfactants being necessary to improve solution stability.
Detergents have employed both physical and chemical methods to increase solubility and stability. Dry powders are made with a spray-dried granule method to increase the speed of dissolution of relevant surfactants and builders. As disclosed by Moore et al in U.S. Pat. No. 4,715,979 (“Granular Detergent Compositions Having Improved Solubility,” 1987), spray-dried granules incorporate multiple concentric layers of constituents with each layer having an increasing surface area that enhances reactivity with the constituents of other layers upon exposure to water. The granular detergent compositions disclosed by Moore et al contain from about 30% to about 85%, by weight of a mixture of C11-C13 alkylbenzene sulfonate surfactant and C12-C16 alkyl sulfate surfactant in a weight ratio of sulfonate surfactant to sulfate surfactant of from about 4:1 to about 1:4.
As the concentration of surfactants has increased in liquid laundry cleaners, solution stability has become an issue with problems of gelation and separation of liquid ingredients. Smadi et al in U.S. Pat. No. 6,376,446 (“Liquid Detergent Composition,” 2002) address synthetic detergent compositions to overcome limited solution stability. They disclose a synthetic laundry detergent comprising a) an anionic surfactant at a concentration from about 5% to about 55% on a weight percentage basis; b) a nonionic surfactant at a concentration from about 10% to about 55% on a weight percentage basis; c) an alkylamine ethoxylate surfactant at a concentration from about 5% to about 55% on a weight percentage; d) a polyalkylene glycol at a concentration from about 1% to about 25% on a weight percentage basis, wherein the polyalkylene glycol has a molecular weight ranging from about 100 to about 5000; and e) an alkylamine. The liquid detergent is phase stable so that gelation and/or visual phase separation does not occur, incorporating surfactants at a concentration of at least 30% on a weight percentage basis. Smadi et al are silent on liquid formulations where soap-based surfactants are utilized. Smadi et al further disclose that their liquid formulations are not stable when the components of the formulation are simply mixed (a simple mixing process includes adding water to the remaining liquid detergent ingredients in one step and then mixing by stirring or shaking); their Example 9 discloses formulations according to their invention that, when mixed together, do not yield stable solutions. They detail orders of addition and mixing methods (high shear mixing, for example) that are successful to produce the stable solutions of their invention (Column10: lines 8-45, and Example 1).
U.S. Pat. No. 4,247,424, “Stable Liquid Detergent Compositions,” issued to Allen et al (1981), discloses liquid detergent compositions which contain an ethoxylated alcohol or ethoxylated alkyl phenol nonionic surfactant, an amine oxide surfactant, a water-soluble detergency builder, a hydrophobic emulsifier and water, with the resulting liquid detergent compositions being stable emulsions. A critical element in the formulation of the stable liquid detergent compositions is the selection and use of a hydrophobic emulsifier. Emulsifiers that are suitable for the stable liquid detergent compositions include lecithin. Allen et al disclose that “the level of hydrophobic emulsifiers required to maintain emulsion stability depend on the nature and level of other ingredients, particularly the ethoxylated nonionic surfactant. A preferred level is from about 5% to about 16% by weight of the total composition”. As disclosed by Allen et al, the detergent formulation provides a precisely controlled chemical environment with very few alkaline metal ions; this is an environment that is optimal for lecithin to function as an emulsifier. Allen et al are silent as to the use of lecithin as an emulsifier in other detergent compositions. Allen et al implicitly teach against the use of lecithin in laundry cleaners that consist entirely of soap-based surfactants by disclosing only surfactant systems that provide a chemical environment with very few alkaline metal ions; soap-based surfactant systems are rich in alkaline metal ions.
Some liquid fabric softeners and laundry detergents incorporate lecithin and lecithin-like compounds in their formulations. Lecithin is added to a fabric softening formulation to act as an organic softening agent, as noted in U.S. Pat. No. 4,808,320A (Alain Jacques and Patrice Pirotton, “Fabric softening compositions based on lecithin and methods for making and using same”). The dispersion of lecithin in an aqueous medium is, however, notably difficult with several references pointing out that the simple mixing of lecithin with an aqueous solution does not successfully lead to dispersion of the lecithin. Such references propose the addition of an emulsifying agent, such as noted in U.S. Pat. No. 3,257,331A (Richard Jameston and Russell Eversole, “Lecithin composition”). Jameston and Eversole note that lecithin is neither soluble nor readily dispersible in water, and teach the addition of an oil emulsifier containing ethylene oxide. U.S. Pat. No. 3,069,361A (George Cogswell, “Water-dispersible lecithin”) similarly addresses the difficulty of dispersing lecithin in aqueous solutions, and teaches the addition of phenoxypolyalkylated alchohols as a dispersion agent.
Lecithin has been suggested as a possible, though not ideal, emulsifying agent, as in U.S. Pat. No. 4,247,424 (Allen et al, “Stable liquid detergent compositions”). The use of lecithin as an emulsifying agent is limited, however, to liquid detergent solutions which include ethoxylated nonionic surfactants. The liquid detergent solutions have a chemical environment with very few alkaline metal ions, an environment virtually required for the lecithin's function as an emulsifier and its continued stability. Allen et al teach against the use of lecithin in a liquid laundry cleaner that is rich in alkaline metal ions, and do not suggest that such use of lecithin would produce a stable liquid solution in an alkaline metal ion rich environment. Implicitely, Allen et al teach against the use of lecithin in a soap-based formulation, as soaps produce an alkaline metal rich environment.
A soap-based laundry cleaner mix, route to market, mixing method, and kit are presented in U.S. patent application Ser. No. 13/136,377, entitled “LAUNDRY CLEANING PRODUCT,” incorporated herein by reference. The laundry cleaner formulation of that invention comprises a dry powder and/or particulate mixture to be added to water to form a liquid laundry cleaner in a mixing container. The dry mixture comprises enzymes such as protease and amylase, soap (acting as a detergent and surfactant), borax decahydrate (acting as a builder and a buffer), and sodium carbonate monohydrate (acting as a builder). The soaps of that invention include sodium salts of carboxylic acids, with the soaps comprising those made via hot processes (boiled and semi-boiled) as well as those made using cold processes. The laundry cleaner formulations that are presented as examples in U.S. patent application Ser. No. 13/136,377 are developed so that when mixed with water in a mixing container, the dry formulation dissolves upon shaking or stirring. It is noted that the laundry cleaner formulations of U.S. Ser. No. 13/136,377 may include emulsifiers (see US 2012/0031804 A1, para 0030, for example).
Laundry cleaner formulations and methods of mixing have been disclosed beyond the patent arts (for example, “LoveToKnow Cleaning” web site with recipe for “Homemade Laundry Detergent”). These formulations consist of dry ingredients that are added to water to form liquid laundry cleaning solutions. Ingredients consist of grated soap (Fels Naptha, most commonly), Borax, and Washing Soda. The method of mixing requires the soap to be melted in water, over heat, with the remaining dry ingredients added and simmered in the liquid to assure mixing. Limitations of such formulations and methods include 1) the dry ingredients and water must be heated to enable adequate mixing; 2) the resulting colloidal emulsion is heterogeneous, with aggregation of gels that make the solution difficult to pour; and 3) the emulsion that results from the addition of the dry ingredients with water may become unstable with particulates falling out of suspension.